This application claims the right of priority of German patent application No. 199 23 680.1, filed May 22, 1999, the disclosure of which is incorporated herein by reference.
The invention relates to a method for determining the operating time and the operating condition of a hydraulic percussion unit such as a hydraulic hammer, comprising a percussion piston which moves inside a housing and alternately performs an operating stroke in a hammering direction and a return stroke. The invention furthermore relates to a device for practicing the method.
Hydraulic percussion tools, in particular hydraulic hammers, are used for crushing material (e.g. for crushing rock or concrete). During the crushing process, the kinetic energy of a percussion piston when it strikes a tool is introduced via the tool and the tool tip into the material to be processed and the kinetic energy is converted into destructive actions. Depending on the hardness of the material to be processed, only a portion of the kinetic energy is converted to destructive action. The remaining, non-converted energy share is reflected via the tool back into the percussion piston. With soft material, on the other hand, the percussion energy is converted completely into destructive actions.
Hydraulic percussion units of the aforementioned type, disclosed, for example, in German Patent No. 34 43 542, (to which corresponds U.S. Pat. No. 4,646,854) represent highly stressed devices that require extensive monitoring and corresponding care and maintenance in consideration of their economy and operational safety, particularly in view of the otherwise heavy-duty operating conditions. Of essential importance in this connection is the operating time of the hydraulic percussion unit, that is to say the information on the total time span during which the hydraulic percussion unit has been actively used.
It is an object of the invention to provide a method and apparatus for determining the operating time and the operating condition of a hydraulic percussion unit, so as to be recognizable in particular to an operator. The personnel in charge thus can decide whether the unit is already in need of maintenance operations or whether the respective percussion unit can continue to be used.
This object and others to become apparent as the application progresses, are accomplished by the invention, which makes use of the realization that the actual total number of hammer strikes carried out by the percussion unit represents a relevant variable for determining the active operating time. Information on the operating condition of the respective percussion unit can be inferred from the total number of hammer strikes by comparison with corresponding specified values. The information relating to the operating condition in the simplest case can be indicated by the completion of a maintenance-free operating interval, which thus indicates a need for maintenance.
A method according to the invention for determining the operating time and the operating condition of a hydraulic percussion unit provides the feature that a number of signals are generated during the individual, chronologically following operating periods of the percussion unit which are proportional to the strokes carried out by the percussion piston in one movement direction. The number of signals is continuously added up and is stored as a total number, and the current total number for the signals is shown at least at times in the form of a display indicating the operating condition. The above-addressed display can be of an optical and/or acoustic nature within the framework of the invention. For example, by generating a continuous acoustic warning signal, it is possible to indicate that an operating condition requiring maintenance exists once a specified total signal number is reached.
The total signal number may be continuously added upxe2x80x94independently of a possible display concerning the operating conditionxe2x80x94and stored, so that it can also be determined to what degree a predetermined maintenance interval has been exceeded by continuing to operate the hydraulic percussion unit.
The type of signals and the manner in which they are generated is optional within the framework of the invention, as long as it is ensured that their number provides information on the number of strokes carried out by the percussion piston in one movement direction. The signals may be generated with the aid of a sensor, which detects physical processes or related changes in condition occurring as a result of the percussion piston movements.
The signals are preferably generated in dependence on at least one of the following physical processes: pressure, motion, sound level, temperature, flow and vibration. However, the invention can also be embodied further in that the actual total number of signals, detected in the previously mentioned manner, is provided with a correction factor in dependence on at least one other influencing variable, e.g. the measured outside temperature. Thus, the display indicating the end of a maintenance interval is triggered at an earlier point in time if a specified outside temperature is not reached.
With a particularly simple embodiment of the method according to the invention, pressure fluctuations or flow processes are detected, which occur in one of the supply lines for the percussion unit, namely the pressure line for the fluid entering the percussion unit and the return-flow line for the return flow of the exiting fluid. In this embodiment, pressure fluctuations or changes in the flow ratexe2x80x94which occur periodically in dependence on the percussion piston strokesxe2x80x94can be converted to signals by means of a pressure monitor or by means of a flow rate meter. These embodiments further have the advantage that they can be installed at a later date without special expenditure and independently of the remaining structural design of the hydraulic percussion unit.
However, the method can also be realized in that the signals that are proportional to the percussion piston strokes are generated on the basis of a sound measurement or by detecting vibrations. For the first type of measurement, a sound transmitter such as a microphone can be used and, if necessary, followed by a suitable, downstream-connected filter. For the second case, the vibrations triggered by the percussion piston movements can be detected by means of a vibration transmitter. This vibration transmitter comprises a vibration sensor that vibrates in the manner of a seismic mass and which cooperates with a plunger coil. The vibration sensor is stimulated to move relative to the plunger coil by the vibrations emanating from the percussion unit. As a result, signals corresponding to the vibrations are generated inductively.
Alternatively, the method can also be realized by detecting with a motion sensor the displacement of a percussion unit component that moves in one movement direction as a result of the percussion strokes. In the simplest case, the movements of the percussion piston itself can be converted into respective signals by an induction coil surrounding the percussion piston without contacting the same. The induction coil is preferably arranged at that side of the percussion piston which faces away from the percussion piston tip.
Within the scope of the invention, the method can also be realized in that the stress exerted on one component of the percussion unitxe2x80x94which stress changes periodically with the hammering actions carried out by the percussion pistonxe2x80x94is detected by means of a force sensor or a voltage sensor. Sensors designed as strain gauges or as piezo elements can be used for this purpose, to convert the occurring stress conditions into signals. In the simplest case, the respective sensors are installed on the percussion unit housing in such a way that they are also deformed by the stress caused by the percussion piston strokes.
If the hydraulic percussion unit is provided with a gas cushion that supports the percussion piston, suitable signals can be generated by detecting the temperature or pressure of the gas cushion by means of a temperature sensor or a pressure monitor. Since the gas cushion is normally arranged on the side of the percussion unit that is opposite the percussion piston tip, these sensors (temperature sensor, pressure monitor) are located relatively far from the direct operating range of the percussion unit.
The method is preferably improved further in consideration of the aspects of operational safety and economy, by providing that once a predetermined total signal number is reached, at least one maintenance display is generated, which indicates at least that the percussion unit requires maintenance. In particular, this can involve a warning lampxe2x80x94for example, of red colorxe2x80x94that lights up and indicates the end of a maintenance-free service interval.
It is also possible to generate in timely succession several early warning indicators depending on the current total signal number. These indicators can show that partial segments of the maintenance interval defined by a predetermined upper limit for the total signal number have been reached.
The above early warning indicators can include a green warning light that lights up initially and, at a later time, a yellow warning light that lights up prior to reaching an upper limit for the predetermined total signal number. As a result, it is possible to detect in stages the actual operating condition of the percussion unit.
Additional advantageous embodiments of the method utilize wireless transmission. Among others, these embodiments make it possible to provide the essential information at a location that is spatially removed from the percussion unit.
Batteries or accumulators can be used to generate the electrical energy required to make the signals available, including obtaining, adding up and storing the signals. For such purpose the energy units should be provided with a charge indicator to avoid malfunctions. The electrical energy for providing the signals may be generated by the fluid that drives the percussion piston. In particular, the unit provided for supplying electrical energy can comprise an auxiliary hydraulic motor and a generator driven by the motor, as well as a downstream-connected electric storage unit.
Alternatively, the electrical energy for providing the signals can also be generated by a generator, which becomes effective as a result of the movements triggered by the percussion piston strokes and which has a downstream-connected electric storage unit. The basic design of such an independently operating generator can correspond in particular to the previously mentioned vibration sensor.
The objects of the invention are furthermore solved by a device which generates a number of signals proportioned to the number of strokes performed by the percussion piston. The device can be provided with a sensor that converts into signals physical processes occurring as a result of the percussion piston movements.